A pistol which fired compressed air bullets, upon impact the
bullets would force out air a inflate it's target.

Use

Kananga took the shark gun off Bond when he was captured, he
then mocked the weapon and fired a bullet into a couch, in which
Whisper was lounging and the couch inflated dumping the overweight
henchman onto the floor. Later Bond got hold of one of the bullets
forcing it into Kananga's mouth, which inflated, his body exploding
into pieces.